Method and system for sensing removal of a utility meter from its socket

ABSTRACT

A method and system is disclosed for indication and prevention of tampering with an electricity meter having control circuitry for automatic remote reading. The control circuitry, provided externally of the meter in a base or base extension, to which the meter is connected, is also used for tamper detection. Embodiments of the invention include use of optical sensing, voltage detection and proximity detection. Ambient light sensing may be performed to detect separation of the meter from the external receptacle. Reflected light to a reflective surface of the meter is sensed to determine if the meter is properly engaged. Presence of a meter connection plug element may be sensed either optically or by position responsive switch. Voltage of the utility supply and meter user output may be monitored to determine tampering.

This application is a continuation of application Ser. No. 07/741,006,filed on Aug. 6, 1991, entitled METHOD AND SYSTEM FOR SENSING REMOVAL OFA UTILITY METER FROM ITS SOCKET, now abandoned.

TECHNICAL FIELD

The present invention relates to remote detection of unauthorizedremoval of an electricity meter from its socket in a plug-in base unit.More particularly, a sensing unit and a microprocessor, removed from themeter housing in an extension of the meter base, is provided to monitorpresence or absence of the meter and to transmit a signal indicative ofmeter removal to a remote location.

BACKGROUND ART

Electricity meter reading technology has developed in recent years toinclude, in addition to traditional manual reading of a meter dial, acapability for remote reading. In a customary remote readingarrangement, optical sensing of the meter rotor is performed. Controlcircuitry is provided for sensor energization and detection, andcorrelation thereof to power usage. Signals indicative of power usageare transmitted to a remote location of the utility company.

Meters generally are enclosed as a unit within a housing which isprovided with a plug to be inserted into a socket of a base. The meteris connected electrically between the utility company power supply sideand the user, or customer, power supply side, both connections beingmade through the base. Such an arrangement is exemplified by U.S. Pat.No. 4,588,949, issued to Becker et al. on May 13, 1986. Automatic meterreading utilizing an optical shaft encoder with appropriate controlcircuitry is illustrated in U.S. Pat. No. 4,665,359, issued to Goodwinon May 12, 1987.

In recognition of the concern of electric utility companies to avoid thetheft of electricity, some conventional meter systems include provisionsfor attempting to determine whether tampering with an electricity meterby unauthorized personnel has occurred. Electricity meters which containelectronic circuitry may contain a position sensitive switch to senseremoval of the meter from its socket. The meter of the above-identifiedBecker et al. patent includes such a device. In the Becker arrangement,removal of the meter and reinstallation thereof actuates a solenoidwhich results in visual indication within the meter display of theunauthorized removal.

As meter reading systems have become more sophisticated, it has beenadvantageous to house the electronic control circuitry in the metersocket base or an extension thereof. Such placement enables easieraccess to the circuit elements in comparison to the enclosed meterhousing which is preferably standardized and may be limited in space toinclude only the structural elements of the meter.

A disadvantage with the placement of electronic components in a baseoutside the meter is that no position sensitive switch, such as providedby the Becker device, or other tampering indicator is available in themeter. If a position sensitive switch is provided instead in the base,additional components must be made available for indication of thetampering condition. Moreover, a position sensitive switch, which candetermine close structural engagement between the meter and base, wouldnot indicate that the connection between meter plug and base socket ismade in proper orientation. For example, if there is an unauthorizedremoval of the meter and then reinstallation in reverse connection, onlythe removal would be indicated. Power usage during such a connectionwould drive the meter rotor in a direction opposite to the appropriatedirection. An actual decrease in the power usage display would occur.Manual meter reading by the utility company at a later time would notreveal this condition.

In the Goodwin meter, tampering is detected by comparing the quantitydisplayed with the encoded values in the optical encoders. Other tamperprevention or detection schemes involve visually discerning the ruptureor breakage of a structural element, such as a lock or seal, associatedwith the meter housing and base. Discovery of tampering with such metersrequires the physical presence of personnel at the meter sites, adisadvantage in terms of cost and time consumption.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the invention is to enable remote detection ofmeter tampering with the efficient utilization of control circuitry usedfor power usage reading.

Another object of the invention is to enable detection of metertampering by use of a sensing device and circuitry located outside themeter housing.

A further object of the invention is to sense removal of an unmodifiedelectricity meter from a meter socket using sensors located within ameter socket base or socket base extension.

Yet another object of the invention is to provide a tampering indicationif a meter is removed from its socket and a tampering indication also ifthe meter is reinstalled in reverse orientation, such provision beingachieved with little or no modification of the meter structure.

The above and other objects of the invention may be satisfied byproviding tamper sensing capability as part of an electricity meterreading system having a microprocessor controlled meter interrogationunit which is housed within a meter base extension. Such unit permitsremote reading of the meter. Detection of removal of the meter from themeter base extension may be made in conjunction with additional meansfor detecting if the meter and meter base extension as a unit is removedfrom the socket in the meter base itself.

Tampering detection, using components external to the meter, may beundertaken in several specific embodiments. A first detection schemeaccording to the invention makes use of an optical sensing arrangementmounted within the meter base extension. Emitted light, directed to areflective surface of the meter housing, is used by the control circuitmicroprocessor to determine the presence or absence of the meter. Only aportion of the meter housing surface is reflective, such portionpositioned to face an adjacent light emitting source in the baseextension only if the meter is connected with the base extension in theproper orientation. If the connection is reversed, the meter will be inan upside down position, the reflective portion being in non-alignmentwith the optical light path. In response to the optical sensor, atampering indication signal is generated when the meter is not connectedto the base extension and when the meter is connected in an impropermanner.

In another embodiment of the present invention, a bayonet type plug andbayonet guard is provided to permit connection between meter and baseextension only in the appropriate orientation. An optical emitter anddetector pair is provided in the base extension to establish a lightpath which, when connection between meter and base extension is made,includes the bayonet or bayonet guard positioned to block emitted lightfrom the detector. Removal of the meter from the extension base permitsthe emitted light to be sensed and, thereby, tampering to be detected.Alternatively, the optical elements may be replaced by a switch locatedin the base extension which is responsive to insertion or removal of thebayonet plug. The switch either opens or closes a sensing circuit toindicate tampering.

Where minimization of the number of circuit components and cost aredominant considerations, an embodiment of the invention provides anoptical detector placed in the meter base extension. If the meter isremoved, ambient light is sensed, indicating meter tampering.

In an alternative arrangement of the invention, a determination oftampering is made by sensing a lack of voltage at the meter, or userside, while concurrently sensing a voltage applied at the utilitycompany side. Such detection indicates removal of the meter. As themeter interrogation unit, used normally to determine power usagereading, derives its power from the utility side the supply voltagethereof can be readily determined.

In an additional embodiment of the invention, the electronic circuit inthe meter base extension includes a metal detector which detects theproximity of the meter frame.

Additional objects and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description, wherein only the preferred embodiments of theinvention are shown and described, simply by way of illustration of thebest mode contemplated of carrying out the invention. As will berealized, the invention is capable of other and different embodiments,and its several details are capable of modifications in various obviousrespects, all without departing from the invention. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a first embodiment of a meter tamperingdetection circuit, according to the invention, illustrating an opticalsensor unit situated external to the meter whereby emitted light isdirected to a reflective surface of the meter housing.

FIG. 2 is a schematic diagram of a meter tampering detection circuitaccording to the invention, illustrating an external optical sensor unitexternal to the meter which detects the presence or absence of the meterconnection plug.

FIG. 3 is a schematic diagram of a meter tampering detection circuitaccording to the invention wherein a switch in a sensing circuit isactuated by the meter connection plug.

FIG. 4 is a schematic diagram of a meter tampering detection circuitillustrating an optical sensor, arranged to detect ambient light in theabsence of the meter.

FIG. 5 is a schematic diagram of a meter tampering detection circuitaccording to the invention wherein both utility line voltage and userline voltage are sensed.

FIG. 6 is a schematic diagram of a meter tampering detection circuitaccording to the invention wherein a metal detector, normally in closeproximity to the meter, senses the presence or absence of the meter.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates a first embodiment of the invention wherein the metertampering circuit is provided external to the meter housing. Theelectricity meter is contained in a housing 10. The back plate of themeter housing 12 includes plug extensions provided to mate with asocket, not shown, in a base extension 15 which is external to the meterhousing 10, and into which the meter is plugged. A reflection surface 14is provided on a portion of the back plate.

The tampering detection circuit 15 is included entirely within the baseor base extension and external to the meter. A sensing unit includeslight emitting diode 16 and phototransistor 18. The light emitting diode16 is connected between a voltage supply V_(CC) and ground through aseries connection of switching transistor 20 and resistor 22. Thephototransistor 18 is connected between the voltage supply V_(CC) andground through the series connection of resistor 24.

An output of microprocessor 32 is connected to supply driving signalpulses to the switching transistor 20. The sensor output voltage, whichis the voltage at the junction of resistor 24 and phototransistor 18, isdirectly connected to a detector input terminal of microprocessor 32.The microprocessor provides functions in addition to tamper detectionwhich are not aspects of the present invention, such as meter usagereading and remote transmission signals indicative of power usagereading.

The application of driving pulses to transistor 20 enables the emissionof light pulses by the light emitting diode 16. If the meter isconnected with the base extension in the proper orientation, the lightpulses are reflected by the reflective surface 14 to the phototransistor18. Light pulses sensed by the phototransistor 18 render it conductivein a saturated mode, thereby connecting the detector input of themicroprocessor to ground. Nonconduction of the phototransistoreffectively disconnects the microprocessor input from ground, wherebythe supply voltage is applied to the detector input of themicroprocessor. The signal at the detector input terminal, therefore, isa bilevel logic signal.

If the meter is removed from its socket in the base extension, lightpulses will not be reflected to the phototransistor. Likewise, if themeter is installed in the upside down position, there will be no lightreflection to the phototransistor as the reflective portion 14 of themeter back plate is not in the light path of the emitted pulses in sucha connection. Many standard meters include an optically reflectivehanger appropriately located. Such hangers may be used for thereflective surface 14 without need to provide additional modification tothe meter.

The voltage at the microprocessor detector input is sensed during boththe on periods and the off periods of the emitter driving pulses. Suchoperation ensures accurate tampering detection during both daytimeambient light conditions and nighttime ambient light conditions. If themeter is removed during a period of high ambient light, light will besensed during the off periods of the emitter driving pulses. Suchsensing indicates tampering as the meter, in the connected state,obstructs ambient light from the phototransistor. If the meter isremoved during a period of low ambient light, the absence of light willbe sensed during the on periods of the emitter driving pulses as thelight emitting pulses are not reflected to the phototransistor. Suchsensing is also a tamper indication. The same results are obtained ifthe meter is reconnected with the base extension in an upside downorientation. The voltage applied to the microprocessor input isindicative of the sensed condition of the optical sensing unit.

FIG. 2 illustrates an alternative embodiment. A bayonet type plug andbayonet guard are provided to permit connection between meter and baseextension only in the appropriate orientation. Phototransistor 18 ispositioned to be directly in the light path of light emitting diode 16,both within the confines of the base extension. Plug element 34obstructs the light path when the meter plug is inserted in the baseextension socket. Detection at the microprocessor input of a voltagerepresenting impingement of the emitted beam or ambient light at thephototransistor is indicative of meter tampering.

In the embodiment of FIG. 3, the optical sensing unit is replaced by aswitch 36, the position of which is dependent upon the plug element 34.Switch 36 is normally closed and is part of a series electricalconnection which also includes the supply V_(CC), resistor 24 andground. The microprocessor input is connected to the junction betweenthe resistor 24 and one terminal of the switch. The arm of switch 36 ispositioned within the base extension to be in the open circuit conditionby the plug element 34 when the meter plug is inserted in the baseextension socket. A tampering condition is thus indicated at themicroprocessor input when the voltage thereof is at ground potential.

FIG. 4 illustrates a further embodiment of a meter tampering detectionarrangement according to the invention. As in the circuit shown in FIGS.1 and 2, phototransistor 18 is connected between the voltage supplyV_(CC) and ground through the series connection of resistor 24. Themicroprocessor input is connected to the junction between the resistor24 and the phototransistor. The phototransistor is physically positionedat the surface 38 of the base extension. When the meter is engaged withthe base extension ambient light paths to the phototransistor areobstructed. When the meter is removed from the base extension duringdaytime conditions of high ambient light, the phototransistor isconductive and the ground potential that is thereby applied to themicroprocessor input terminal is indicative of a meter tamperingcondition.

FIG. 5 illustrates a meter tampering detection circuit according to theinvention wherein the presence or absence of utility line voltage anduser line voltage are sensed. The meter interrogation unit, includingmicroprocessor 32, which is also used for power usage reading, derivespower from the utility line through transformer 40. Power supply 42 isconnected to the transformer secondary. Voltage on the user line side ofthe meter is detected by an optical isolator, including light emittingdiode 16 and phototransistor 18. Other means, such as an additionaltransformer, may be used in place of the optical isolator.

When the meter is removed, no voltage is applied to the user linethrough the meter. The presence of voltage at the utility line side isdetected from power supply 42 at the microprocessor input. The absenceof voltage at the user line results in nonconduction of thephototransistor, whereby a voltage at the supply voltage level isdetected at the load voltage detect input to the microprocessor. Thedetection of supply voltage states at both microprocessor inputs is anindication of meter tampering. Such indication can be transmitted to aremote location of the utility company.

FIG. 6 illustrates a meter tampering detection circuit according to thepresent invention wherein a metal detection circuit 46 within the baseextension senses the proximity of the meter frame through inductivepickup 44. The metal detector circuit may be any of well known availablecircuits and may include an application specific integrated circuit inthe meter base extension. An output voltage level of the detectorcircuit, which represents absence of the meter, is an indication ofmeter tampering.

In summary, there has been disclosed several methods and circuitarrangements for the detection of electricity meter tampering whereinsuch detection is determined externally of the meter. Remoteinterrogation of the external circuit may be made by the utility companyto monitor the tampering condition.

In this disclosure there is shown and described only the preferredembodiments of the invention and but a few examples of its versatility.It is to be understood that the invention is capable of use in variousother combinations and environments and is capable of changes ormodifications within the scope of the inventive concept as expressedherein.

What is claimed is:
 1. A method for ascertaining tampering of aconnection between an electricity meter, of the type which includes plugextensions which plug into respective sockets in a base external to saidmeter, and an external base to which said electricity meter is connectedand through which external power is supplied to said meter comprisingthe steps of:(a) emitting light pulses from said external base; (b)sensing light reflected by said meter by circuitry solely within saidexternal base; (c) generating a bilevel voltage by said circuitry withinsaid external base, each level corresponding respectively to arelatively bright light condition and a relatively dark condition; and(d) detecting a meter tampering condition in response to said bilevelvoltage.
 2. A device for detecting tampering of a connection between anelectricity meter, of the type which includes plug extensions which pluginto respective sockets in a base external to said meter, and anexternal base to which said electricity meter is plugged and throughwhich external power is supplied to said meter, said devicecomprising:(a) passive means which is part of said meter which canmodify a signal from a source external to said meter; (b) active means,contained solely within said external base, said active means not beinga part of said meter or needing any physical connection to said meterapart from plugging said meter into said external base, said activemeans providing a signal to said passive means; and (c) detecting means,contained solely within said external base for indicating the proximityof said meter to said external base and for thereby detecting that saidmeter has been unplugged from said external base, whereby a tamperingcondition will be indicated.
 3. The device of claim 2 for detectingtampering of a connection between an electricity meter, of the typewhich includes plug extensions which plug into respective sockets in abase external to said meter, and an external base through which externalpower is supplied to said meter, wherein:(a) said passive means includesan optically reflective portion on the rear of said meter; (b) saidactive means comprises light emitting means contained solely within saidexternal base, said active means being capable of emitting light pulses,said light pulses reflecting rom said optically reflective portion onthe rear of said meter when said meter is plugged into said externalbase; and (c) said detecting means comprising sensing means for sensinglight reflected from said optically reflective portion on the rear ofsaid meter and for generating a bilevel voltage, each levelcorresponding respectively to a relatively bright light condition and arelatively dark condition, in response to said sensing means, whereby atampering condition of the type in which said meter is removed from saidbase will be indicated by the absence of reflection of light from saidoptically reflective portion of said meter.
 4. The device of claim 3,wherein said meter is enclosed in a housing including a back plate, saidback plate having a surface at least a portion of which is opticallyreflective;(a) said light emitting means comprises a light emittingdiode; (b) said sensing means comprises a phototransistor positioned ina light path including said light emitting diode and the opticallyreflective portion of the meter back plate.
 5. The device of claim 4,wherein said detecting means comprises a microprocessor including anoutput terminal for supplying driving pulses to said light emittingdiode and an input terminal for receiving said bilevel voltage.
 6. Thedevice of claim 5, wherein said detecting means comprises circuit meansresponsive to a dark condition sensing output of said phototransistor toproduce a tamper indicating signal during periods of light emittingdiode emission and responsive to a light condition sensing output ofsaid phototransistor during periods of non light emitting diodeemission.
 7. The device of claim 3 wherein said optically reflectiveportion comprises the meter hanger which is on the rear of a standardelectricity meter.